This report covers the design, fabrication and initial testing of a linear beam tetrode switch tube. Design goals were 140 kV video output at 100 A load current and 0.08 (0.03 min) duty cycle at pulse lengths up to 300 microsec. Important features are the nonintercepting grid, convergent electron beam passing through the anode (screen grid), high efficiency, and voltage-depressible collector-probe system. Cooling capability of the collector and probe was improved through a new, computer-aided thermal design which retained approximately the same geometry. The collector-probe system was evaluated up to 100 kV video output at 0.03 duty.